Electrodeposition of copper from an acid bath



United States Patent ELECTRODEPOSITION OF COPPER FROM AN ACID BATH Richard A. Fellows, Grosse Pointe, and Edwin W. Hoover and Henry Brown, Huntington Woods, Mich., assignors to The Udylite Research Corporation, Detroit, Mich., a corporation of Michigan Application December 28, 1954, Serial No. 478,178

16 Claims. (Cl. 204-52) No Drawing.

The present invention relates to the electrodeposition of copper from an aqueous acidic bath, and more particularly concerns the utilization of selected addition agents to aqueous acidic baths for the purposes hereinafter stated.

()ne of the primary objects of this invention is the production of electrodeposits of copper having a high degree of luster and brightness as obtained directly from the electroplating bath, and without buffing or polishing as set forth more fully hereinafter in Table 2. r1 Broadly,

the organic compounds which are useful for, .the purposes of this invention may be represented by Formula A.

FORMULA-= A wherein R1 and R are radicals selected 'fron'fthe; grtiup consisting'of hydrogen; methyl andethyl ra'd icalsjfand X is mnion" selected from the gro p consis ti gor clu ride, "bi ontide', iodide, fluoride, sulfate, bisttlfate anemitrat'; and Z is an' aromatic radical selected ffr o'tn tlie groupjconsisting .of phenyl," naphthyl, andfiphe yljzind naphthyl radicals substituted with amino,falkyl'subs tituted "amino, .hydroxy and alkoxy"substituent groups.

"The anion is relatively 'uniin'p'or'tanfand in non to the anions above 'given may be any one of a Wide varietyfof other anion s' iriclu'ding or'ganic" anions; "such ice Patented Mar. 13, 1956 ciated that the compounds represented by the above formula when present in an acid copper bath are highly ioniied substances and the anion X is in ionicadmixture with the other anions-of the bath such as the sulfate anion, the nitrate anion, etc.

Thiourea and acetyl thiourea, as well as the compounds represented by Formula A} have been used separately previously. The use of thioure'a is disclosed in U. 5. Patent 2,489,538 and the compounds represented by Formula A are. disclosed and claimed, in cppending applicatiorffS'erial No. 290,091; 'how'Pa'te'nt 2,707,166.

'Thiourea when used alone sutiers from a number of disadvantages including embrittlemen't ofthe plate at even low concentrations, relatively narrow range of current densities within which brightness is obtained, requirement of low temperature of operation, 'etc. The compounds represented by Formula A when used-alone are incapable of producing a lustrous, bright, deposit; For example, the use of the dye designated briefly as diethyl-safranineazo-dimethyl-aniline, alone in an acidic copper sulfate bathf at its optimum concentration produces a fine-grained plate over a wide range of currentdensity, but the luster and 'brightness are hot of the highest order. Electrode- "posits produced from copp Sulfate baths containing thiourea are dullon all areas in whicli thecurrent density was low or medium or similarly are dull when produced from bathsqjoperating at temperatures abo'veya'bout 75 F. It has now-been surprisingly discovered that the use of both of the above-identified agents in combination gives better eleet-rodeposits, as evaluated both by appearance and leveling properties, and by a decrease in the criti'cality of conditions of operation of the bath, than the use ofeither of them alone.

In actual practice whenthese two compounds are used A together, a brighter'plate over a much wider current 'dens'ity' range is obtained and polishing 'lines 'are almost 4 completely leveledby a deposit having a thickness of approximately .6 mil. to 1 mil.

cordancewith this invention and in the ranges of propor- ?asrermate, acetate, propionate, etc. It "will be a pre- I Furthermore the concentration of the thioureas is less critical, and bath temperatures of F. to F. can be used to produce a truly brilliantdeposit which does not require any 'biiffing off polishing whatsoever to prepare the deposittbr direct "bri heehromium plating. The 'electrodeposits obtained in accordance with this invention have been carefully domipa'i ed with plate produced from baths containing thiourea other addition agents such as molasses, 'dextrin and certain Wetting agents, and the; effect obtained by the tion agents; of this invention far exceeds' the enhance stilts obtained with the molasses, dextrin oi wettingigent combinations. Copper deposits are obtained having the high" degree of brilliance necessary for the production of bright chromium plate directly over the copper. Somewha t better results are obtained, however, by'de'pos'iting abi'ight nickel "plate directly upon the copper plate inits u'rib lied andunpolished condition, and thereafter' platthin bright nickel deposits having thicknesses in the range of approximately .1 mil to .2 mil plated directly on top of the unbufied copper, usually having a thickness ofv .6

injiljto .7 mil, have a luster similar to th a't which isj' ob- Y mined from thick deposits of bright nickel, for example 1 mil? to 'LS mils, plated directly on steel or other metallic surfaces having a comparable initial surfacejcondition. illustrative exa'm'ples of addition agent'siepieseh'tedlb the above given Formula A which may befut'iliz'ed in'actidns" indicated, are given in Table 1.

Table 1 Optimum Cone.

Cone. grams/um grams/liter on GH:

(ClHi)rN N=N-ON-(C m), N v or Diethyl safranlne szo dlmothyl aniline-Janus Green B CH CH:

c,H-),N Nae-Q01;

N CK v Dlethyl safranine no phenol-Janus Black CH CH: H

Sairanine azo naphthol-Janns Blue 4. Janus Gray (Color Index 137, Society of Dyers & Colourlsts, .0015-.05 .015

by M. Rowe, 1924).

5. Dimethyl satranlne azo dimethyl aniline 0015-. 015

Mixtures of the dyes shown in Table 1 may also be employed with beneficial elfects. Where mixtures are employed, however, the total concentration of the mixed dye in the aqueous acidic bath preferably approximates the concentration of any component indicated in Table 1. For general purposes concentrations of the dyes of :Table l falling within the range of .005 to .04 gram/liter represent preferred quantities.

Sulfur compounds which may be used incombination with a compound represented by Formula A or mixtures thereof, in the general ranges of proportions indicated, are set forth in Table 2.

Mixtures of the sulfur compounds of Table'2 may be used in combination with one or a mixture of the compounds of Table 1, and when such mixtures are used, the total quantity of the mixture should fall within the range of about .001 to .05 gram/liter.

Instead of the compounds represented by FormulaA, it is possible to use safranines in conjunction with the thioureas to obtain enhanced brightening of the copper deposit. However, the degree of brightness and leveling action is not as high as that obtained with the use of the compounds represented by Formula A in conjunction with the thioureas of Table 2. Mixtures of the safranines with the compounds represented by Formula A when used in conjunction with the thioureas, also give copper deposits having high brightness. Examples of safranines which have been found to increase the brightness of the copper deposit when used in combination with the thioureas of Table 2 or in admixture with any of the compounds represented by Formula A and the thioureas of Table 2 include phenosafranine, tolusafranine, fuchsia,

amethyst violet, mauveine, diethyl safranine, and di-' methyl safranine. When a safranine or a mixture of safranines is used in conjunction with a compound of Table 2, the concentration of a safranine or a mixture of safranines may vary between about .002 gram/liter to .03 gram/liter and preferably is maintained in the range of .003 gram/liter to .01 gram/liter. In admixture with the compounds of Formula A and the compounds of Table 2, safranines are preferably used in minor quantities, for example, .003 gram/liter safranine in admixture with .012 gram/liter Janus Green B and .003 gram/liter N-propionyl thiourea.

Somewhat superior operating bath life is obtained from' the use of N-trifluoroacetyl thiourea and N-propionyl thiourea at concentrations ranging between .006

and .015 gram/liter, and for this reason these materials represent preferred compounds. Outstanding results have been obtained with the combination of Janus Green B in concentrations of .006 to .015 gram/liter andN-t'ri' 'fluoroacetyl thiourea and N-propionyl thiourea in concentrations of .006 to .015 gram/liter. It is preferable to maintain a concentration of chloride, or its equivalent in bromide or iodide, of about .003 to about .020

gram/liter in the solution. It is to be understood that as FORMULA B Preferred "Coma; grams/Ute:

he lConca grams/liter Other well-known acidic" copper platin'g baths m'ay' 'b'e ,used satisfactorily. Other copper salts such as copper 's'ulfarnate, coppef fluoborate, copper methyl sulfonat'e and Leopper 'ethyllsulfonate' may be used asa substitute for or .an adjunct to" the copper sulfate ofthe' above forman. The useof these substitute copper saltsfienables somewhat higher speed plating than is possible fromthe copper sulfate bath. For best results when using any of these substitute copper" salts; -somewhat smaller concentrations are preferred, for 'example; 50 l'50" grams'l liter.

The-preferred conditionsof operation-of-baths ="containing proportions ofaddition agents indicated in Table 1- include controlled--temperatures 1 bath agitation" and c'ath'ode" current densities. ---For example; the bath tem- '-per aturesmaybefrom about 1 7" C". to C (approximately 70 F. to 105 F.). The warmer t'emper'atures above 40 C. tend to decrease; the'brightness of the plate,

' that temperaturesiiupltofiOLC. may be used-satisfactorily.

when X is eitherfluoride,- sulfate;-l'iisulfate or nitrate, that; chloride, bromide or 'iodide'ions'iii an- ;am um equivalent to about .003 -.020 gram/litefiofchlorideis preferably present inyaddition. As ini'tially made11p;- a solution containing; a'compound-inwhich Xis a halide other than fluoride, contains at ;leas't'the preferredfminimum halideconcentration; but it -'is-=usually preferable :Gathode agitation and ..prefe1:ably uniform. airagitation ist}. desirable:; vCathode. a current densities of 10''l'00 amps/sqwft; (approximately l-loxampsilsqsidmJi may be satisfactorily-1.iernployed: with; the: particular current \density dependingprimarily. nponvthe degree of agita'tion iofatlie .cath'odenfilmmandutheashapebfathe 'a'rticle t 6 plated. For t general: purposes and l average'cathode cur rent density of 30-50 amps/sq. ft. may ber'us'edl As a substitute for therssulfuric acid of Formula B, tnitric acid orphosphoric acid may be useddnqapproxi- ;mately equivalent proportions. Additionally, Formula ;Bt=:may :inclu deother ions for the purpose .of-vincreasing the conductivityr -lof the solution such :assodiumypotats sium or ammoniumtions. 1 These ionsareusuallyspresent in only minor concentrations. Furthermore; thencopper sulfate of Formula B may be replaced by coppensnitrat'e :in approximately equivalent proportions; =andr when acidi tied with small amounts of phosphoric acid nitric acid or sulfuric acid, the beneficiahetfect; of reducing the grain ,size and increasingrthe luster of the deposit by additions .ofsmall" concentrations ofco mpounds of the type shown in Table 11 is also evident. The degree,.however,- -.-0f vgrain size, reduction and increase in luster is somewhat lessrexterisive' than is produced from the use of acidic baths made up primarily of coppersulfate. Ingeneral, thecopper sulfate or copper nitrate concentration in-vthe bath may satisfactorily vary from asvlowzas aboutwt grams/liter up to saturation. .Concentrations of acid above the equivalent in acidity of about 80400 grams/liter of sulfuric. acid decrease the brightening effect of the. addition agents.represented by Formula A andfare, therefore to be avoided.

,Smal ljconcentrations.ofwetting agents may bet'advantage'ously. present .in :the baths. ofthis: invention: For example, the surface active. compounds,- sodium-decyl sulfate and the sodium salt of sulfated monoethylene glycol ether of decyl alcohol: when present in small concentrations of about 0.1 to .'06"gram/liter are effective in decreasing pitting and striation formation in the deposit due to thepresence of harmfulorganic compounds or excessive concentrations of brighteners; These Wetting agents normally cause vexcessive frothing with air agitation, but in the presenceof the addition agents of Table l, the frothing is minimised.

The following typical plating baths are given by way of example to illustrate the invention in greater'detail:

Air agitation. What is claimed is:

'1. A bath for the electrodeposition of copper comprising an aqueous acidic solution of copper salts, a safranine, minor proportions of at least one compound selected from the group consisting of thiourea, N-acetyl thiourea, N-propionyl thiourea, N-trifiuoroacetyl thiourea, N-pentafluoropropionyl thiourea, N-furfuroyl thiou- 'rea, dimethyl thiourea, cyanoacetyl thiourea, and a compound having the structure:

EXAMPLE I @800 SHzO "grams/liter" 200 H2804 do 15 Janus Green B ..-do .015 Thiourea do .010 Temperature F" -95 'Cathode current density ..amps./sq. ft-.. 30-40 Air agitation.

EXAMPLE II CuSOs-SHzO -grams/liter 200 H2804 15 Janus Green B ..do .010 N-trifiuoroacetyl thiourea ..do- .006 Sodium N-decyl sulfate ..do .01-.03 Temperature F..- 70-95 Cathode current density amps./sq. ft 30-40 Air agitation.

EXAMPLE III CuS04-5H20 "grams/liter..- 200 NH4NO3 do 20-30 H2804 (10..-..- 15 Janus Green B do .015 N-propionyl thiourea ..do .001 Temperature F-.. 70-95 Cathode current density ..amps./sq. ft..- 30-50 Air agitation.

EXAMPLE IV Cu(N03) grams/liter 200 HNO3 10 Janus Black do .010 N-furfuroyl thiourea do .015 Sodium salt of sulfated monoethylene glycol ether of decyl alcohol grams/liter-.. .0l-.03

Temperature F-.. 70-95 Cathode current density amps./sq. ft 30-50 Air agitation.

EXAMPLE v CuS04-5H20 grams/liter 200 H2804 do 15 ,Janus Green B do .006-.015 N-pentafluoropropionyl thiourea -do .02 Sodium salt of sulfated monoethylene glycol ether of decyl alcohol grams/liter .01-.03

Temperature F..- 70-95 Cathode current density amps./sq. ft 30-40 "Air agitation.

' EXAMPLE VI 'ClISO4-5H2O grams/liter 200 H2504 l5 Janus Green B do.. .05 'Dimethyl thiourea do. .03 Temperature F 70-95 Cathode current density amps./sq. ft 30-40 wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino, hydroxy and alkoxy substituent groups.

2. A bath for the electrodeposition of copper comprising an aqueous acidic solution of copper salts, from .001 to .05 gram/liter of at least one compound selected from the group consisting of thiourea, N-acetyl thiourea, N-propionyl thiourea, N-trifluoro acetyl thiourea, N- pentafluoropropionyl thiourea, N-furfuroyl thiourea, dimethyl thiourea, cyanoacetyl thiourea and .0015 to .05 gram/liter of a compound having the structure:

wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate; and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino, hydroxy and alkoxy substituent groups.

3. A bath for the electrodeposition 'of copper comprising an aqueous acidic solution of copper salts and minor proportions of at least one compound selected from the group consisting of Janus Green, Janus Blue, Janus Black, Janus Gray and dimethyl safranine azo dimethyl aniline and at least one compound selected from the group consisting of thiourea, N-acetyl thiourea, N-propionyl thiourea, N-trifiuoro acetyl thiourea, N-pentatluoropropionyl thiourea, N-furfuroyl thiourea, dimethyl thiourea and cyanoacetyl thiourea.

4. A bath for the electrodeposition of copper comprising an aqueous acidic solution of copper salts and .0015-.05 gram/liter of at least one compound selected from the group consisting of Janus Green, Janus Blue, Janus Black, Janus Gray and dimethyl safranine azo dimethyl aniline, and .001.05 gram/liter of at least one compound selected from the group consisting of thiourea,

'N-acetyl thiourea, N-propionyl thiourea, N-trifluoro acetyl thiourea, N-pentafluoropropionyl thiourea, N-furfuroyl thiourea, dimethyl thiourea and cyanoacetyl thiourea.

5. A bath for the electrodeposition of bright copper consisting essentially of copper sulfate, sulfuric acid, .00l5-.05 gram/liter of Janus Green B, and .001-.05 gram/liter of N-trifiuoro acetyl thiourea.

6. A bath for the electrodeposition of bright copper consisting essentially of copper sulfate, sulfuric acid, .00l5-.05 gram/liter of Janus Green B and .00l-.05 gram/ liter of thiourea.

7. A bath for the electrodeposition of bright copper consisting essentially of copper sulfate, sulfuric acid, .00l5-.05 gram/liter of Janus Green B and .00l-.05 gram/ liter of N-acetyl thiourea.

8. A bath for the electrodeposition of bright copper consisting essentially of copper sulfate, sulfuric acid, .0015-.05 gram/liter of Janus Green B and .001-.05 gram/liter of N-propionyl thiourea.

, 9. A bath for the electrodeposition of bright copper consisting essentially of copper sulfate, sulfuric acid,

.0015-.05 gram/liter of Janus Green B and .001-.O gram/ liter of N-furfuroyl thiourea.

10. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic solution of copper salts, said aqueous solution also containing a safranine and minor proportions of at least one compound selected from the group consisting of thiourea, N-acetyl thiourea, N-propionyl thiourea, N-trifluoroacetyl thiourea, N-pentafiuoropropionyl thiourea, N-furfuroyl thiourea, dimethyl thiourea, cyanoacetyl thiourea and a compound having the structure:

wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino, hydroXy and alkoxy substituent groups.

11. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic solution of copper salts, said aqueous solution also containing minor proportions of at least one compound selected from the group consisting of Janus Green B, Janus Black, Janus Gray, Janus Blue, dimethyl safranine azo dirnethyl aniline and at least one compound selected from the group consisting of thiourea, N-acetyl thiourea, N-propionyl thiourea, N-trifluoroacetyl thiourea, N-pentafluoropropionyl thiourea, N-furturoyl thiourea, dimethyl thiourea and cyanoacetyl thiourea.

12. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic solution of copper salts, said aqueous solution also containing .0015.05 gram/liter of a compound selected from the group consisting of Janus Green, Janus Blue, Janus Black, Janus Gray and dimethyl safranine azo dimethyl aniline, and .001-.05 gram/liter of a compound selected from the group consisting of thiourea, N-acetyl thiourea, N-propionyl thiourea, N-trifiuoroacetyl thiourea, N- pentafluoropropionyl thiourea, N-furfuroyl thiourea, dimethyl thiourea and cyanoacetyl thiourea.

13. In a process of electrodepositing copper, the step which comprises electrolyzing an aqueous acidic solution of copper salts, a halide selected from the group consisting chloride, bromide and iodide in an amount equivalent to about .003 gram/liter to about .020 gram/liter of chloride, and minor proportions of a compound having the structure:

wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl and phenyl and naphthyl radicals substituted with amino, a kyl substituted amino, hydroxy and alkoxy substituent groups, and at least one compound selected from the group consisting of thiourea, N-acetyl thiourea, N-propionyl thiourea, N-trifluoroacetyl thiourea, N-pentafluoropropionyl thiourea, N-furfuroyl thiourea, dimethyl thiourea and cyanoacetyl thiourea.

14. A bath for the electrodeposition of copper comprising an aqueous acidic solution of copper salts, a halide selected from the group consisting of chloride, bromide and iodide in an amount equivalent to about .003 gram/liter to about .020 gram/ liter of chloride, and minor proportions of a compound having the structure:

wherein R1 and R2 are radicals selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate; and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino, hydroXy and alkoxy substituent groups, and at least one compound selected from the group consisting of thiourea, N-acetyl thiourea, N-propionyl thiourea, N-trifluoroacetyl thiourea, N-pentafluoropropionyl tbiourea, N-furfuroyl thiourea, dimethyl thiourea and cyanoacetyl thiourea.

15. A bath for the electrodeposition of copper comprising an aqeous acidic solution of copper salts and .0015-.05 gram/liter of at least one compound selected from the group consisting of Janus Green, Janus Blue, Janus Black, Janus Gray and dimethyl safranine azo dimethyl aniline, .001.05 gram/ liter of at least one compound selected from the group consisting of thiourea, N-acetyl thiourea, N-propionyl thiourea, N-trifluoroacetyl thiourea, N-pentafluoropropionyl thiourea, N-furfuroyl thiourea, dimethyl thiourea and cyanoacetyl thiourea and a small amount of a wetting agent.

16. In a process of electrodepositing copper, the step Which comprises electrolyzing an aqueous acidic solution of copper salts, said aqueous solution also containing .0015 to .05 gram/liter of a compound selected from the group consisting of Janus Green, Janus Blue, Janus Black, Janus Gray and dimethyl satranine azo dimethyl aniline, .001 to .05 gram/liter of a compound selected from the group consisting of thiourea, N-acetyl thiourea, N-propionyl thiourea, N-trifluoroacetyl thiourea, N-pentafl1ioropropionyl thiourea, N-furfuroyl thiourea, dimethyl thioures. and cyanoacetyl thiourea and a small amount of a wetting agent.

References Cited in the file of this patent UNITED STATES PATENTS 2,291,590 Lind et al. July 28, 1942 2,326,999 Lind et a1. Aug. 17, 1943 2,602,774 Beaver July 8, 1952. 2,707,166 Brown et al. Apr. 26, 1955 

1. A BATH FOR THE ELECTRODEPOSITION OF COPPER COMPRISING AN AQUEOUS ACIDIC SOLUTION OF COPPER SALTS, A SAFRANINE, MINOR PROPORTIONS OF AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF THIOUREA, N-ACETYL THIOUREA, N-PROPIONYL THIOUREA, N-TRIFLUOROACETYL THIOUREA, N-PENTAFLUOROPROPIONYL THIOUREA, N-FURFUROYL THIOUREA, DIMETHYL THIOUREA, CYANOACETYL THIOUREA, AND A COMPOUND HAVING THE STRUCTURE: 